Automatic alignment system



K. ENsLElN 2,727,994

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Dec. 20, 1955 K. ENSLEIN AUTGMATIC ALIGNMENT SYSTEM 16 Sheets-Shee 16 Filed Feb. 5, 1951 United States Patent O 2,727,994 AUTORIATIC ALIGNMENT SYSTEM Kurt Enslein, Rochester, N. Y., assigner, by niesne assignments, to General Dynamics Corporation, a corporation of Delaware Application February 5, 1951, Serial No. 209,357 33 Claims. (Cl. Z50-40) The present invention relates to an alignment system for automatically aligning electrical circuits, and, more particularly, to an improved system for accurately and quickly tuning resonant circuits to a predetermined fre quency. Specically, the present invention is an improvement on the automatic alignment method and apparatus disclosed and claimed in applicants copending application, Serial No. 157,160 filed on April 20, 1950, now Patent 2,584,004, and assigned to the same assignee as the present invention.

In many instances, it is necessary to align an electrical circuit to a predetermined frequency. For example, each of the radio and television receivers which are now being produced in great volume include a number of resonant circuits which lnust be tuned to the correct operating frequencies. Up to the present time, the alignment of such resonant circuits is performed manually by trained operators. Each operator views the response of each resonant circuit on an oscilloscope, or on an indicating meter, and manually tunes the resonant circuit to the correct frequency as indicated by a maximum or peak response of the resonant circuit. Such an alignment procedure is inherently laborious and time consuming and requires skilled personnel to manipulate the test equipment and interpret the data obtained. While a human operator can align a single resonant circuit with good accuracy and in a relatively short period of time, when he attempts to align resonant circuits one after the other, he is unable to operate with any acceptable speed or accuracy over long periods of time. Consequently, when tunable circuits are aligned manually, the results are unreliable and are very non-uniform. ln some instances, the resonant circuits, when manually tuned, may be as much as 30% olf in amplitude from the desired peak response point, which resuits in an inferior receiver and in non-uniformity in the receivers produced. 'it is, therefore, desirable to have a fully automatic alignment system wherein resonant circuits can be accurrately, reliably and uniformly aligned to the correct operating frequencies. Also, it is desirable to decrease the time required to tune each circuit to the correct operating frequency without employing highly skilled technicians so that more receivers can be tuned in a given period of time and the expense of operating personnel can be reduced.

It is, accordingly, an object of the present invention to provide a new and improved apparatus for automatically aligning electrical circuits to predetermined frequencies.

l't is another object of the present invention to provide a new and improved apparatus for automatically tuning resonant circuits to predetermined frequencies which is particularly suitable for use by unskilled operators on a production line basis.

t is a further object of the present invention to provide a new and improved apparatus for automatically aligning electrical circuits to predetermined frequencies which is particularly suitable for use by unskilled operators and wherein alignment may be accomplished with a high degree of accuracy.

lt is a still further object of the present invention to provide a new and improved apparatus for automatically aligning electrical circuits to predetermined frequencies wherein such alignment may be accomplished by unskilled operators in a minimum amount of time on a production line basis and with a high degree of uniformity of the aligned circuits.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

Fig. l is a schematic diagram in block diagram form of an automatic alignment system embodying the present invention;

Figs. 2(n)2(c) inclusive, 8(0), 8(1)) and 9(a)9(d) inclusive are timing diagrams illustrating the operation of certain portions of the system of Fig. l;

Figs. 3-7 inclusive and Figs. 10-15 inclusive are detailed schematic diagrams of portions of the automatic alignment system of Fig. 1;

Fig. 16 is a schematic diagram in block diagram form of an alternative alignment system embodying the present invention;

Fig. 17 is a detailed schematic diagram of a portion of the system of Fig. 16;

Fig. 18 is a schematic digram in block diagram form of a further alternative alignment system embodying the present invention; and

Figs. 19 to 26 inclusive are detailed schematic diagrams of portions of the system of Fig. 18.

Referring now to the drawings and more particularly to Fig. l thereof, there is illustrated in block diagram form one alignment system embodying the present invention which is capable of accurately aligning resonant circuits to a predetermined frequency on a fully automatic basis and with very much less time expended than with manual alignment. The automatic alignment system is shown in connection with a modulated carrier wave receiver, indicated generally at 10 which contains a plurality of resonant circuits which are to be aligned to a predetermined frequency, one of which circuits is illustrated at 15, and comprises an inductance coil 16 and a condenser 17. A fixed frequency alignment signal generator 11 is connected to the receiver 19 over the conductor 11a and supplies an alignment signal to the resonant circuit 15 at the frequency to which the circuit 1S is to be tuned.

While the resonant circuit 15 may be energized by any suitable means from the preceding stage in the receiver, in the illustrated embodiment the inductance 16 is shown as the secondary winding of an interstage transformer 22, the primary of transformer 22 being connected to the anode ofthe preceding amplifier tube 23. The resonant frequency, or tuning, of the resonant circuit 15 is varied by any suitable means such as the tuning slug 24 which is movable within the coil 16 of the resonant circuit to change the inductance thereof and tune the circuit 15 continuously through a band of frequencies which includes the predetermined frequency with which the circuit 1S is to be aligned. Movement of the tuning slug is done under the control of a reversible driving motor 25 which drives a suitable tool 26, such as a screw driver or the like, which engages the tuning slug 24. The tool 25 may be engaged with the tuning slug 24 either manually by the operator or by means of automatic or semi-automatic positioning apparatus. The speed and direction of rotation of the motor 25 are controlled by the alignment system of the present invention, as will be described in more detail hereinafter.

When a xed frequency signal is supplied to the resonant circuit 15 in the manner described above the resonant frequency of the circuit 15 is varied by moving the tuning slur` 24 in a predetermined direction, the signal produced across the resonant circuit will vary in accordance with the well known resonance phenomenon and will be a maximum when the resonant frequency of the circuit corresponds exactly to the frequency of the alignment signal, or, in other words, when the circuit 15 is at peak resonance. The signal thus produced across the resonant circuit 15 is detected in the detector circuit including the rectifier 18, the load resistor 19 and the filter condenser 21, to provide a unidirectional voltage which is proportional to the instantaneous response of the resonant circuit 15, the detector output voltage being used as an input signal for the alignment system proper.

Generally considered, the automatic alignment apparatus of Fig. l aligns the circuit 15 with the frequency of the signal generator 11 by first moving the tuning slug 24 past the maximum or peak resonance point of the circuit 15 to establish a sustained reference voltage which is proportional to the response of the circuit 15 at the desired peak resonance point. After the peak resonance point is passed and the reference voltage has been established, the direction of movement of the tuning slug 24 is reversed and tuning of the circuit 15 is controlled in accordance with the difference between the reference voltage and the instantaneous voltage across the circuit 15 so that the circuit is tuned back to its peak resonance point. When the reference voltage and the instantaneous response of the circuit 15 agree, the circuit 15 is tuned correctly and movement of the tuning slug is halted. Inasmuch as the reference voltage once established must be maintained substantially without change during the alignment cycle it may be called a memory Voltage and this voltage will be thus referred to hereinafter.

To accomplish the above-described alignment operations the automatic alignment system comprises a memory system which in general performs the function of establishing the memory voltage which is proportional to the peak response of the circuit 15 and a motor control system which in general performs the function of controlling the speed and direction of rotation of the motor 25 so as to tune the circuit 15 in the manner described above.

The memory system includes a comparison bridge 3f), a chopping circuit 31, a gating amplifier 36, a switching circuit 37, and a memory circuit 38. The memory circuit 38 includes a storage element in the form of a memory storage condenser having a very high leakage resistance so that the condenser once charged will not lose any appreciable charge for the remainder of the alignment cycle. Charging of the memory condenser is controlled by the instantaneous resonant circuit voltage so that the voltage across the memory condenser follows the resonant circuit voltage up to the peak response point and thereafter remains at peak voltage to provide the sustained memory signal described above.

The comparison bridge performs the function of comparing the instantaneous response voltage of the circuit 15 with the voltage across the memory condenser of the circuit 38 to provide an error output signal equal to the difference between these voltages. To perform this function the comparison bridge 30 is supplied with lan input signal from the detector load circuit 19 and 21 over the conductor 12 and with memory voltage from the memory circuit 3S over the conductor 14.

The chopping circuit 31 performs the function of converting the error output signal from the comparison bridge 3@ into a square wave of proportionate amplitude and sense. Thus, when the resonant circuit Voltage is greater than the memory circuit voltage, the square wave produced by the chopping circuit 31 is of a given polarity and has an amplitude proportional to the difference between these voltages. When the resonant circuit voltage is less than the memory circuit voltage the square wave produced by the chopping circuit 31 is of the opposite polarity and has an amplitude proportional to the difference between these voltages. To perform the above described function l the chopping circuit 31 receives the output of the comparison bridge 30 over the conductor 13 and is controlled by a standard oscillator 39 which supplies a control voltage to the chopping circuit 31 over the conductor 29 to control the generation of the above-described square wave.

The square wave produced by the chopping circuit 31 is supplied to the gating amplifier 36 over the conductor 20a and the unit 36 performs the function of passing only square waves of one polarity. Specifically, the gating amplifier 36 passes only a square wave of the polarity which is produced when the instantaneous resonant circuit voltage is greater than the memory condenser voltage. To perform this function the gating amplifier 36 is controlled by a square wave generator 41 which latter unit supplies a square wave of positive polarity to the gating amplifier over the conductor 40 and is itself controlled by the standard oscillator 39.

The switching circuit 37 in general performs the function of controlling the intervals during which the memory storage condenser of the memory circuit 3S is charged from an independent voltage source. To perform this function the switching circuit 37 is turned on under the control of the gating amplifier 36 which supplies a keying pulse to the unit 37 over the conductor 27 to initiate charging of the memory storage condenser. The switching circuit may be turned o by either one of two different systems to effect either a sequential or a coincidence type of charging of this condenser. In the sequential system of charging the memory condenser the condenser is charged by definite increments until the memory condenser voltage is equal to the detector voltage at which time the charging intervals cease. In the coincidence system of charging the memory condenser the condenser is continuously charged, once the charging circuit is turned on, until the memory condenser voltage coincides with the detector voltage at which time a coincidence signal is derived which is used to turn off the switching circuit 37 and halt charging of the memory condenser. In the system illustrated in Fig. l the switching circuit 37 is so connected as to effect a sequential type of charging of the memory storage condenser. More specifically, the switching circuit 37 is turned off under the control of a positive square wave supplied from the square wave generator 41 over the conductor 40. A coincidence system of charging the memory condenser is shown in Fig. 16 and will be described in more detail in connection therewith.

In order to control the driving motor 25 in a manner to tune the circuit 15 initially through the peak response point and thereafter tune the circuit 15 back to the peak response point under the control of the memorized reference voltage produced in the manner described above by the memory circuit 3S, there is provided the motor control system which includes the comparison bridge Si?, the chopping circuit 31, an A. C. amplifier 32, a balanced keyed rectifier circuit 33, a differential D. C. amplifier 34, a differential relay 35, a starting circuit 42, a reversing counter circuit 45, a reversing relay circuit 43 and a motor driving circuit d4.

The starting circuit 42 includes the starting switch 5% which, upon closure, initiates the alignment cycle and performs the functions of supplying an independent control voltage at the start of the alignment cycle to cause the motor 25 to tune the circuit 15 through and beyond its peak resonance point by a predetermined amount and of thereafter removing the independent control voltage and substituting therefor the balanced output from the differential D. C. amplifier 34. The starting circuit 42 also performs the function of internally unbalancing the differential relay 35 at the start of the alignment cycle. To perform these functions the starting circuit 42 is connected to the reversing relay circuit 43 over the conductors 52 and 52a and to the differential D. C. amplifier 34 by means of the conductors StB and 50a.

The square wave produced by the chopping circuit 31 is also supplied to the A. C. amplifier 32 over the vconductor 29 which latter unit performs thc function of amplifying the square wave to a suitable value. The output of the A. C. amplifier is supplied to the balanced keyed rectifier circuit 33 over the conductor 48 which latter unit performs the function of reconverting the amplified square wave into a pair of balanced unidirectional control voltages. To perform this function the balanced keyed rectifier 33 is supplied with both positive and negative square waves from the square wave generator 41 over the conductors 40 and 47.

The differential D. C. amplifier 34 is connected to the balanced keyed rectifier circuit 33 over the conductors 49 and 49a and performs the function of amplifying the output thereof and supplying amplified balanced control voltages to the differential relay 35 over the conductors 50 and 50a. The differential D. C. amplifier also performs the additional function of supplying balanced control voltages to the starting circuit 42 over the conductors 50 and 50a to control the motor 25 after the circuit 15 is tuned beyond its maximum response point by a predetermined amount.

The differential relay 35 is controlled by the differential D. C. amplifier 34 and the starting circuit 42 and performs the function of controlling the starting circuit 42 to remove the independent control Voltage from the motor 25 when the circuit is tuned beyond its peak resonance point by a predetermined amount. The differential relay also performs the function of supplying a control pulse over the conductor 51 to the reversing counter circuit 45 each time the circuit 15 is tuned through the peak response point.

The reversing relay circuit 43 is controlled by the reversing counter circuit 45 and the starting circuit 42 and performs the function of reversing the polarity of the balanced control voltages supplied thereto from the differential D. C. amplifier 34 each time the tuned circuit 15 is tuned through its peak response point to effect re versal of the motor and hence of the direction of tuning of the circuit 15. To perform this function the reversing relay circuit 43 is connected to the starting circuit 4?. by means of the conductors 52 and 52a; to the reversing counter circuit 45 by means of the conductor 55 and to the motor driving circuit 44 by means of the conductors 53 and 53a. The motor driving circuit supplies current to the split field windings of the motor 25 over 'the conductors 54 and 54a to control the speed and direction of rotation thereof and thereby control the tuning of the circuit 15.

OPERATION OF THE SYSTEM OF FIG. l AS A WHOLE Briefly to consider the general mode of operation of the automatic alignment system of Fig. 1 described above, the alignment cycle is started 'oy depressing the starting switch 500 which energizes the starting relay of the starting circuit 42. When the starting relay of the circuit 42 is energized there is produced an internal unbalance in the differential relay which causes this relay to close in a predetermined direction and thereby to close a holding circuit which holds the starting relay closed after the starting switch 50d is released. Energization of the starting relay also causes an initialdriving-voltage of predetermined magnitude and polarity to be supplied to the motor driving circuit 44, whereupon the motor 25 drives the tuning slug 24 in the correct direction to tune the circuit 15 toward its peak response point. in this connection it will be understood that the tuning slug 24 may be positioned at one extremity of the coil 16 before the start of the alignment cycle and the polarity of the voltage supplied to the motor 25 so chosen that the tuning slug moves into the coil 16 so as to tune the circuit 15 in the correct direction.

As the resonant frequency of the circuit 15 is varied in the manner described above, the voltage produced across the detector load circuit 19 and 21 becomes increasingly negative with respect to ground potential as the resonant frequency of the circuit 15 approaches more closely the frequency of the alignment signal from the gene erator 11. If the tuning slug is moved completely through the coil 16 the gradually changing detector voltage takes the form of a conventional resonance curve having a maximum or peak which corresponds to the alignment signal frequency as will be readily apparent to those skilled in the art.

Assuming that the output from the comparison bridge 30, as initially adjusted, is equal to Zero at the start of the alignment cycle, as the detector voltage increases negatively in the manner described above, the negative output from the comparison bridge causes the memory condenser to be charged until the voltage across the memory condenser is equal to the detector voltage at which time the output from the comparison bridge is equal to its initial or zero value and charging of the memory condenser is halted. As the detector voltage continues to increase negatively, the memory voltage increases in the manner described above and effectively follows the detector voltage up to the peak response point. However, after the peak response point is passed the detector voltage becomes increasingly less negative whereas the memory condenser remains charged to the maximum negative detector voltage so that the output from the comparison bridge becomes positive with respect to its initial value and continues to increase positively as the circuit 15 is tuned further and further beyond the desired peak response point.

The output from the comparison bridge is then used to rebalance the differential relay 35 and reverse the direction of rotation of the motor 25 after which the cornparison bridge output is used as an error signal to control the speed of the motor 25 so as to tune the circuit 15 back to its peak response point. To accomplish these functions, the increasing positive voltage produced by the comparison bridge 30 as the circuit 15 is tuned further beyond the peak response point, is converted into a square wave of corresponding amplitude and sense in the chopping circuit 31, amplified in the A. C. amplifier 32, and reconverted in the balanced keyed rectifier 33 into a pair of balanced unidirectional control voltages which are further amplified in the differential D. C. amplifier 34 and supplied to the differential relay 35 in the proper polarity to overcome the internal unbalance of the differential relay produced at the start of the alignment cycle. Accordingly, when the circuit 15 has been tuned beyond its peak response point by an amount sufficient to overcome the internal unbalance initially given to the differential relay 35, this relay opens, the initial driving voltage is removed from the motor driving circuit 44 and the amplified error signal from the differential D. C. amplifier 34 is substituted therefor and is used to control the tuning of the circuit 15 back to its peak response point. Also, when the differential relay 35 opens, the internal unbalance initiaily made therein is removed and the differential relay closes in the opposite direction due to the continued application of the error signal applied thereto from the differential D. C. amplifier 34.

When the motor 25 has tuned the circuit 15 back to its peak response point the error signal from the comparison bridge 3f), which now controls the motor 25, falls to zero and the motor stops with the tuning slug positioned at the desired peak response point. if the mechanical driving system possesses sufficiently low inertia, the driving motor stops precisely at the peak resonance point and the alignment cycle is completed. However, if the mechanical system possesses substantial inertia, as is the practical case, the driving motor will not stop when the error signal from the comparison bridge reaches Zero but instead will coast beyond the peak response point and an error signal is again produced by the comparison bridge. The polarity of this error signal produced by overshoot of the motor 25 is still of positive polarity due to the fact that the detector voltage becomes positive with respect to the memory voltage on both sides of the peak response point. Accordingly, it is necessary to reverse the polarity of the error signal each time the circuit is tuned through the peak response point in order to effect reversal of the motor and tune the circuit 15 back to its peak response point. This last mentioned function is performed by the differential relay 35, the reversing counter circuit 45 and the reversing relay circuit 43. Thus, the positive error signal from the comparison bridge, which is amplified in the units 31, 32, 33 and 34 in the manner described above, goes to zero each time the circuit 15 is tuned through the peak response point. Each time the error signal goes to zero the differential relay 35 opens and thereafter closes in the same direction as the error signal becomes increasingly positive after the peak response point is passed. Each time the differential relay 35 opens and closes it produces a control pulse which is used to control the reversing counter circuit and effect a reversal of the reversing relay 43 which in turn reverses the polarity of the amplified error signal which is supplied from the differential D. C. amplifier 34 to the motor driving circuit 44.

If the driving system again overshoots the peak response point the polarity of the voltage supplied to the motor driving circuit 44 is again reversed as the differential relay opens and closes when passing through the Zero error signal or peak response point. Such operation continues until the output from the differential D. C. amplifier is insufficient to drive the motor 25 at which time the tuning slug is accurately positioned at the maximum response point of the circuit 15.

ln order to render the mode of operation of the automatic alignment system of Fig. l more readily understandable, there is shown in Figs. 2(a) and 2(5) the detector voltage and memory voltage characteristics produced in the system of Fig. l. Referring to Fig. 2(a) the voltage produced across the detector load circuit 19 and 21 of the receiver 10 is therein illustrated and is plotted as a function of time. The initial voltage across the resonant circuit 15 coincides substantially with zero or ground potential, vas indicated by the line 60, thus indicating that the resonant frequency of the circuit 15 is so far removed from the frequency of the signal generator 11 that there is substantially no response by the resonant circuit at lthis frequency. As the tuning slug is moved in the direction of the peak response point in the manner described heretofore, the detector voltage increases in the negative direction as indicated by the curve 61. After the peak response point is reached, which point is illustrated in Fig. 2(a) as occurring at the time ti, the detector voltage again decreases as indicated by the curve 62.. It will be seen from an examination of Fig. 2(a) that the portions 61 and 62 of the detector voltage curve constitute a segment of the conventional single peaked resonance curve of a resonant circuit as it is tuned through resonance.

As the detector voltage builds up in the negative direction as indicated by the curve 61 in Fig. 2(a), the voltage across the memory condenser follows the detector voltage as illustrated in Fig. 2(1)). Referring to Fig. 2(b), the memory condenser is initially short-circuited as hereinafter explained so that there is Zero voltage across it as indicated by the line 70. As the detector voltage increases in the negative direction, the voltage across the memory condenser also increases along the curve 71. However, after the peak response point is reached, which point is again illustrated in Fig. 2(b) as occurring at the time t1, the voltage across the memory condenser remains constant as indicated by the portion 72. Thus the memory condenser voltage may be utilized as a reference voltage indicative of the peak response of the tunable circuit 15.

Referring again to Fig. 2(a), when the tuning slug is moved beyond the peak response point by an amount sufcient to produce a positive error signal from the comparison bridge 30 of sufficient amplitude to overcome the original internal unbalance made in the differential relay 35, this relay opens. The first opening of the differential relay 35 is illustrated in Fig. 2(11) as occurring at the time t2 at which time the detector voltage is positive with respect to the memory circuit voltage by an amount A which is sufficient exactly to balance the differential relay and cause it to open. When the differential relay opens at time t2 the internal unbalance is removed and the relay closes in the opposite direction and effects reversal of the motor 25 so that the circuit 15 is tuned back toward the point of maximum response. Accordingly, the detector voltage increases negatively again along the line 63 until it is again equal to the memory circuit voltage at time ts. lf the mechanical driving system possesses very little in ertia the tuning slug will not be driven beyond the peak response point 64 and hence the circuit 15 is accurately aligned to the desired peak response point.

lf the driving system possesses substantial inertia, the tuning slug will be driven beyond the maximum response point 64 and the detector voltage will again increase along the opposite slope of the response curve as indicated at 65. When the tuning slug is overdriven so as to produce a positive response as indicated at 65, the differential relay again closes, having previously opened as the maximum response point 64 is reached, and supplies a control pulse to the reversing counter circuit 45 to effect reversal of the reversing relay 43 and reverse the direction of movement of the tuning slug. lf the direction of movement of the tuning slug were not reversed, the positive going voltage 65 would tend to drive the tuning slug further away from the maximum response point 64. However, when the differential relay is closed after passage through the maximum response point 64, the reversing counter circuit 45 is actuated in the manner described above so that the direction of movement of the tuning slug is again reversed at time ri. The tuning slug is thus successively reversed at times Z4 and f5 as it passes back and forth through the peak response point and the tuning slug eventually comes to rest at a position such that the detector voltage is exactly equal to the memory voltage and the circuit 15 is tuned exactly to peak resonance.

DETAILED DESCRIPTION OF THE SYSTEM OF FIG. 1

in considering the detailed circuitry of the system components briefly described above, operation of these components will be analyzed in so far as possible in terms of the functions which they perform in tuning the resonant circuit 15 to the alignment signal of the generator 11. Before considering the details of the system components, however, it is pointed out generally that corresponding reference characters have been used throughout the drawings to identify corresponding circuit elements of the system. lt is also pointed out that while single conductors have been illustrated as inter-connecting the units shown in block diagram form in Fig. 1, all of the units are connected to the common ground potential indicated in each of the detailed schematic diagrams. Furthermore, unless necessary to an understanding of the operation of a particular system component,v those circuit elements which perform entirely conventional functions in the circuit, namely functions which will be readily understood by those skilled in the art, have not been identified in the drawing nor referred to in the following description of the system components.

Comparison bridge 30 As previously pointed out in the general description of the system of Fig. l, the comparison bridge 3ft, which is shown in detail in Fig. 3 of the drawings, performs the function of comparing the detector voltage derived from the tunable circuit 15 and a voltage derived from the memory circuit 3S and provides an output voltage equal to the difference therebetween. The output from the detector load circuit 19 and 21 is connected over the conductor 12 to the comparison bridge circuit 30 and 

